A radial pump is known from the book "Die Pumpen Arbeitsweise Berechnung Konstruktion", 13., neubearbeitete Auflage", published by Springer-Verlag Berlin Heidelberg New York 1977, FIG. 74.5 of Hellmuth Schulz. In this case the connecting part is designed as in the case of a crosshead internal combustion engine, i.e. it is composed of a piston-cylinder guide which is connected at one side to the eccentric by means of a drive rod and at the other side to the pump piston by means of a fixed pin which carries out only a to and fro movement. This produces a complex construction with a large number of bearing points. All these bearing points have to be lubricated. If adequate lubrication cannot be ensured, rolling bearings must be used. This involves a large amount of space and more noise during rotation. Although rolling bearings have lower requirements as regards lubrication than plain bearings, it nevertheless remains necessary to provide lubrication.
European Patent Specification 0,165,876 discloses a radial pump in which no sleeve is fitted on the eccentric and the pistons run as cam followers on the eccentric. Although the large number of bearings mentioned above is not necessary in such a design, it does mean that the lubrication requirements are greater, due to the surfaces of the piston and the eccentric moving along each other. It is also necessary to provide special means for moving back the piston. In the European patent this is achieved by means of coil springs. The disadvantage of this is that control of the return movement is difficult to manage at higher speeds of rotation, certainly if a low spring pressure is being aimed at, in order to limit the power consumption by the pump as much as possible.
A radial pump according to the preamble of claim 1 is known from FR-A-2123032. From this specification frictional engagement of the plunger to the sleeve is known. The plunger is urged against the sleeve by means of a resilient leaf spring. Several of such leaf springs are provided and each leaf spring connects to opposite positioned plungers and is for that reason circular shaped. No further support for each circular leaf spring is provided. This means that return movement of the plunger is controlled by spring characteristics of the leaf springs. The eccentric to which the end of the plunger engages will not only urge the plunger to-and-fro but will also displace laterally relative to the contact face between the plunger and the sleeve surface. This means that there will be some friction between the sleeve and the plunger end.